1. Field of the Invention
The present invention relates to a probe for use in measuring a biological signal and a biological signal measuring system incorporating the probe.
2. Description of the Related Art
Pulsation (i.e., pulse) and blood pressure, like human metabolism, vary among individuals. In addition, blood components, blood volume, and pulsation intensity vary at measuring sites of a subject, and even at the same measuring site depending on when the measurement is performed and the subject's physical state. Accordingly, reliable biological signal measuring devices with the ability to provide accurate biological information on a subject are required. Such a measuring device may be a probe that provides information, such as a photoplethysmogram.
Biological signal measurement sites should not cause stress to a patient subjected to a biological signal measurement, but should allow measurement of a faint biological signal from a patient's body. For these reasons, biological signals are commonly measured at a patient's finger.
Pulsation is the most commonly measured biological signal. The elasticity of blood vessels that reach a fingertip, blood circulation status, and weakness of blood vessels all can be measured from a fingertip pulsation measurement. In addition, arterial and peripheral blood vessel disorders can be diagnosed at an earlier stage.
Methods of measuring pulsation, which indicate the beating status of the heart, blood vessel status, and blood circulation status, can be classified into blood pressure measurement and photoplethysmography. Blood pressure measurement refers to the measurement of a change in blood pressure in a blood vessel using a noninvasive sensor. Photoplethysmography refers to the-measurement of blood volume change in a peripheral blood vessel, using an intensity of a light transmitted through a predetermined site on the subject's body.
Conventionally, a photoplethysmogram of a subject can be measured at the subject's finger using a probe. However, it may not be known whether the subject's fingernail accurately contacts a light source of the conventional probe. More specifically, light may radiate onto a skin site, not a fingernail and noise may be incorporated into a resulting photoplethysmogram. Although the fingernail may contact the light source, noise components from external light or external circumstances may be generated if the contact pressure between the fingernail and the light source is insufficient, i.e., not within a proper range, thus leading to unreliable diagnosis results.